Optical information recording apparatus

ABSTRACT

A rewritable optical disk apparatus, optical information recording and reproducing apparatus or the like is allowed to automatically and properly adjust the optical system to the optimum focal condition regardless of the readout signal detector&#39;s positional error and the residual aberration in the optical system. The spherical aberration and defocus are coarsely adjusted using the amplitude (PP amplitude) of the tracking error signal and then finely adjusted using the amplitude (RF amplitude) of the readout signal. Since the spherical aberration can properly be adjusted, it is possible to raise the reliability of the readout signal.

CLAIM OF PRIORITY

The present application claims from Japanese application JP 2003-329296filed on Sep. 22, 2003, the content of which is hereby incorporated byreference into this application.

BACKGROUND OF THE INVENTION

The present invention relates to optical disk media and opticalinformation recording apparatus which use light to write/readinformation to/from recording media. In particular, the inventionrelates to an optical information recording apparatus capable ofcorrecting the sphericalh aberration.

With the progress in density of optical disks and other opticalrecording media, a typical optical system is employing a largernumerical aperture with shorter wavelength light. Accordingly,aberration due to manufacturing errors of lenses and recording media isbecoming a critical problem. For example, the spherical aberration dueto the thickness error of a cover layer on a recording medium sharplyincreases in proportion with the fourth power of the numerical apertureif wavelength is fixed. In addition, the influence of aberration becomeslarger in reverse proportion with wavelength λ if manufacturing errorsand other conditions are the same.

Owing to these factors, recent high density optical informationrecording apparatus are required to have optical heads provided withspherical aberration correcting capability. Note that in thisspecification, “optical information recording apparatus” is used torefer to an apparatus which records or reproduces information to or froma recording medium by using the means to irradiate light to a recordingmedium and the means to detect light from the recording medium.

In the optical information recording apparatus, it is necessary toautomatically adjust both focus and spherical aberration of the lens atthe same time. If the spherical aberration is adjusted (and changed),the apparent focal point (optimum focal length) of the lens changes alittle. (Hereafter, we refer to the intentional change of the focalpoint (focus offset) as ‘defocus.’) To reach an optimum condition, it istherefore necessary to change both spherical aberration and defocusconcurrently.

If either spherical aberration or defocus is not optimized, the beamspot cannot be reduced enough to allow high-density recording. Inaddition, manufacturing fluctuations may add astigmatism to the lens andpositional errors to the photodetector. In this case, the zero point ofthe detection signal is deviated, making it impossible to rely on thesignal voltage in determining the optimum condition. Therefore, atwo-dimensional search or changing both spherical aberration and defocusconcurrently is necessary to find the optimum condition. (Hereafter, werefer to the amount of defocus as ‘defocus value.’)

As such a two-dimensional adjustment method of the spherical aberrationand defocus, Japanese Patent Laid-open No. 2002-324328 has proposed amethod for two-dimensionally searching the respective values in four oreight rectangular directions. However, this method carries thedisadvantage that the search speed is slow and a long waiting time isimposed until a medium becomes available after inserted into the opticaldisk apparatus (drive).

SUMMARY OF THE INVENTION

It is a first object of the present invention to overcome this problemand provide an optical disk apparatus (optical information recordingapparatus) which can adjust the spherical aberration and defocus asquickly as possible so that the user can begin to use an optical disk(medium) without long waiting time after inserted into the optical diskapparatus.

In addition, the prior art methods carry the disadvantage that if anunrecorded disk (medium) is inserted, it is not possible to accuratelylocate the optimum point by using the readout signal (RF amplitude)without being influenced by manufacturing errors since no marks arerecorded.

It is a second object of the present invention to overcome this problemand provide an optical disk apparatus (optical information recordingapparatus) that can accurately optimize the spherical aberration anddefocus even if the inserted disk (medium) is an unrecorded disk.

In addition, by achieving these objects which ease the limit ofmanufacture tolerance, the present invention is intended to provide aninexpensive high reliability optical disk apparatus (optical informationrecording apparatus) capable of recording/reproducing large quantitiesof information at lower cost.

According to the present invention, the spherical aberration and defocusare adjusted coarsely using the amplitude of the tracking error signal(PP amplitude) and then adjusted finely using the amplitude of thereadout signal (RF amplitude). Since changing the spherical aberrationin this adjustment changes best focus offset (defocus) that maximizesthe amplitude of the tracking error signal, both spherical aberrationand defocus are concurrently changed at a constant ratio according tothe change ratio of the defocus to the spherical aberration in order toreduce the time spent for the two-dimensional search.

In addition, when an unrecorded optical disk (optical recording medium)is used, marks are written onto the medium after the amplitude of thetracking error signal is roughly maximized by adjusting the sphericalaberration and defocus. Then, the spherical aberration and defocus arefinely optimized using the amplitude of the readout signal retrievedfrom the written marks.

A specific configuration to implement them is an optical informationrecording apparatus comprising: a first detector for detecting theamplitude of the readout signal; a second detector for detecting theamplitude of the tracking error signal; a first adjustor for adjustingthe spherical aberration; and a second adjustor for adjust the defocusof the objective lens (such as an object lens actuator); wherein beforeand after the amplitude of the tracking error signal is detected, thedefocus and the spherical aberration are automatically changedconcurrently at a constant ratio determined by characteristics of theoptical system in searching for the maximum amplitude of the trackingerror signal. Ideally, the ratio is in the range of ±60% of the Δt/Δzvalue calculated according to the following equation:

$\begin{matrix}{{\Delta\; z} = {{{- \frac{\left( {n^{2} - 1} \right)}{4n^{3}}} \cdot ({NA})^{2} \cdot \Delta}\; t}} & {{Equation}\mspace{14mu} 1}\end{matrix}$Where, n is the refractive index of the transparent layer of therecording layer, NA is the numerical aperture of the objective lens, Δtis a correction of the spherical aberration and Δz is a shift of thefocal length of the objective lens (defocus).

In a two dimensional rectangular coordinate system whose respective axesrepresent the defocus and the spherical aberration, an oblique search ismade at first so as to maximize the amplitude of the tracking errorsignal and then a rectangular search is made so as to maximize theamplitude of the readout signal.

In the case of a rewritable unrecorded optical recording medium isinserted, after adjustment is made to increase the amplitude of thetracking error signal, marks are recorded and then the sphericalaberration is adjusted so as to maximize the amplitude of the readoutsignal.

The recorded marks constitute a repetitive pattern whose mark intervalis 2 to 4 times the track interval in the data area.

In addition, the marks recorded for the purpose of adjustment are erasedafter the amplitude of the readout signal is maximized by adjustment.

According to another aspect of the present invention, optimum sphericalaberration and defocus are preliminarily measured at inner and outertracks or both ends of a medium. Spherical aberration and defocus whichare to be set at an intermediary point for information read/write arecalculated by interpolation based on the preliminarily measured values.Specifically in the case of a recording card medium, the opticalinformation recording apparatus has a memory for storing the optimumspherical aberration values (and optimum defocus values for theobjective lens) which are respectively for four corners on the recordingmedium; wherein the optimum spherical aberration and defocus values foran information read/write position are calculated from the storedoptimum values by interpolation based on the ratios in terms of theposition's distances from the four corners.

In the case of a recording disk medium, the optical informationrecording apparatus has a memory for storing the optimum sphericalaberration values (and optimum defocus values for the objective lens)which are respectively for inner and outer tracks on the recordingmedium; wherein the optimum spherical aberration and defocus values foran information read/write track are calculated from the stored optimumvalues by interpolation based on the track's position.

In the case of a multilayer recording medium, optimum sphericalaberration and defocus are preliminarily measured at inner and outertracks or both end positions in the top and bottom layers. When jumpingto another layer, an offset is calculated by linear interpolation andadded to the set spherical aberration just before the jump. (Whenjumping to another layer, an interpolative value between the valuesmeasured preliminarily for the inner and outer positions is used.)

Specifically, the optical information recording apparatus has a memoryfor storing the optimum spherical aberration values which arerespectively for the top and bottom layers; wherein immediately beforeaccess is moved perpendicularly across one or more recording layers, theoptimum spherical aberration to be set for the target layer iscalculated from the stored optimum values by interpolation.

In addition, each of the aforementioned optical information recordingapparatus can be configured such that: if an initialized (recorded, orformatted) disk (recording medium) is inserted, the adjustment isstarted from optimization for the amplitude of the readout signal; andif an not initialized recording medium is inserted, the adjustment isstarted from optimization for the amplitude of tracking error signal.

Since the spherical aberration can accurately be optimized regardless ofaberrations due to assembling errors and optical components themselves,it is possible to raise the reliability of the readout signal. Alsosince accurate adjustment is possible even with an unrecorded(un-initialized) rewritable optical disk medium (recording medium)according to the present invention, a variety of recording media can beused for recording and reproducing information. In addition, since thepresent invention allows the spherical aberration to be adjusted so asto encompass the resulting shift of the optimum defocus, the waitingtime imposed after a medium is inserted can be shortened, allowing theuser to immediately operate the apparatus.

Accordingly, the present invention can provide a low cost, highrecording density and high reliability easy-to-operate optical diskapparatus capable of treating various types of recording media.

BRIEF DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an example of a procedure for adjusting the sphericalaberration and defocus according to the present invention;

FIG. 2 shows the configuration of an optical information recordingapparatus capable of correcting the spherical aberration according tothe present invention;

FIG. 3 shows an amplitude distribution of the tracking error signal;

FIG. 4 shows an amplitude distribution of the readout signal;

FIG. 5 shows an example of a procedure for adjusting the sphericalaberration and defocus according to the present invention;

FIG. 6 shows an example of a procedure for adjusting the sphericalaberration and defocus according to the present invention;

FIG. 7 shows the configuration of an optical system capable ofcorrecting the spherical aberration to which the present invention isapplicable;

FIG. 8 shows an enlarged contour map indicating an amplitudedistribution of the tracking error signal;

FIG. 9 shows an enlarged contour map indicating an amplitudedistribution of the tracking error signal;

FIG. 10 shows an amplitude distribution of the tracing error signalobtained with presence of astigmatism;

FIG. 11 shows an amplitude distribution of the tracking error signalobtained with presence of coma aberration;

FIG. 12 shows an enlarged contour map indicating an amplitudedistribution of the tracking error signal;

FIG. 13 shows an amplitude distribution of the readout signal obtainedwith presence of astigmatism;

FIG. 14 shows an amplitude distribution of the readout signal obtainedwith the presence of coma aberration;

FIGS. 15A to 15D show how the amplitude distribution of the readoutsignal depends on the recorded mark pattern period;

FIG. 16 is a diagram for explaining a coordinate system assumed for asingle layer disk to which a correcting procedure is applied;

FIG. 17 shows a correcting procedure for a single layer disk;

FIG. 18 is a diagram for explaining a coordinate system assumed for amultilayer disk to which a correcting procedure is applied;

FIG. 19 shows a correcting procedure for a multilayer disk;

FIG. 20 is a diagram for explaining a coordinate system assumed for amultilayer recording card medium to which a correcting procedure isapplied; and

FIG. 21 shows a correcting procedure for a multilayer recording cardmedium.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will thereinafter be described withreference to FIGS. 1 through 21. To facilitate understanding, portionsproviding the same operation are given the same reference numeral in therespective figures.

Embodiment 1

Spherical Aberration/Defocus Adjustment Method for Rewritable OpticalDisk

With reference to FIGS. 1 through 7, the following describes the generalconfiguration of an optical disk apparatus (optical informationrecording apparatus) provided with a spherical aberration correctingfunction according to the present invention.

Firstly, FIG. 2 shows the general configuration of an optical diskapparatus (optical information recording apparatus) provided with aspherical aberration correcting function according to the presentinvention.

(General Configuration of Optical System)

An optical disk 8 or a recording medium is mounted on a motor 10 whoserotation speed is controlled by a rotation servo controller 9. A laserdiode 12 driven by a laser driver 11 irradiates this medium with light.After having passed through a collimating lens 13 and a beam-shapingprism 14, light from the laser diode 12 is guided toward the disk 8 by areflecting mirror 15 which changes the direction of the light. The lightreflected by the reflecting mirror 15 passes through a polarizing beamsplitter 16, a liquid crystal aberration corrector 17 and a quarter waveplate 18. Then, the light is focused on the disk 8 by an objective lens19. The objective lens 19 is mounted on an actuator 20 so that the focalposition can be actuated in the track direction by a signal of atracking servo controller 21 and in the focal direction by a signal of afocus servo controller 22. The liquid crystal aberration corrector 17compensates for the substrate thickness error of the disk 8 and thespherical aberration of the objective lens. A control voltage from aspherical aberration controller 23 causes the spherical aberrationcorrector to have a distribution of the refractive index which differsdepending on the distance from the center of the beam of light so as tocorrect the spherical aberration by compensating for aberrant advancesor delays of the wave front. Correcting the spherical aberration allowsthe beam of light to be converged to an enough small beam spot to read amicroscopic mark pattern recorded on the disk 8 and record a markpattern on the disk 8. The irradiated beam of light is partly reflectedby the disk 8 and passes again through the objective lens 19, thequarter wave plate 18 and liquid crystal aberration corrector 17. Then,the reflected light beam is split toward a cylindrical lens 24 by thepolarizing beam splitter 16. The split light beam goes through thecylindrical lens 24 and the detection lens 25 and reaches four quadrantphotodetectors 26 where the light beam is detected and converted toelectrical signals. A photo-current amplifier 27 amplifies theelectrical signals. By doing addition and subtraction on these signals,a tracking error signal generator 29 generates a tracking error signal,a focus error signal generator 28 generates a focus error signal and areadout signal generator 30 generates a readout signal. The amplitude ofthe tracking error signal is detected by a tracking error signalamplitude detector 32 to output the signal amplitude. The amplitude ofthe readout signal is also detected by a readout signal amplitudedetector 33 to output the signal amplitude. These signal amplitudesignals are received by a correcting signal generator 34. Theconfiguration described so far is the same as the configuration of acommon optical disk apparatus except for the sections concerningspherical aberration correction, i.e., the liquid crystal aberrationcorrector 17, the spherical aberration controller 23 and the correctingsignal generator 34.

The obtained tracking error signal is also supplied to the trackingservo circuit 21 to control the position of the objective lens 19 in thetrack direction. The focus error signal, after added a defocus signal(focal position-correcting signal) by a defocus offset adder 31, issupplied to the focus servo controller 22 to control the defocus valueof the objective lens 19. The readout signal also goes through anequalizer 35, a level sensor 36 and a timing clock generator 37 and isconverted to the recorded original digital signal by a decoder 38. Thesecircuits in a series are controlled in a unified manner by a mainsequencer 39.

The correcting signal generator 34 receives the amplitude of thetracking error signal and the amplitude of the readout signal togenerate the spherical aberration correcting signal and the defocussignal. The following describes how the correcting signal generator 34operates.

(Spherical Aberration Correcting Signal Generator)

According to how the amplitude of the tracking error signal and that ofthe readout signal behave, the correcting signal generator 34 functionsto generate a spherical aberration correcting value and an defocusvalue. The defocus value is an offset to the focus error signal. Thetarget focal position is shifted by the offset from the position atwhich the focus error signal becomes zero. Hereinafter, such a focalposition offset is called a defocus.

FIGS. 3 and 4 respectively show how the amplitude of the tracking errorsignal and that of the readout signal appear with the presence ofspherical aberration. Note that they are ideal conditions obtained byoptical calculation.

FIG. 3 shows how the amplitude of the tracking error signal changesdepending on the spherical aberration and the defocus. Its distribution,like a mountain chain, has a long and narrow peak in an obliquedirection. This indicates that if the focal position is not correct, thetracking error signal has peak points offset from the in-focus positionwhere the spherical aberration is corrected. To reach the highestelongate gentle peak point (the maximum amplitude of the tracking errorsignal), it is therefore necessary to adjust both spherical aberrationand defocus concurrently. However, since the amplitude of the trackingerror signal is likely to fluctuate depending on the tracked place ofthe disk during rotation, this tracking error signal-used adjustment isdifficult to obtain a sufficient adjustment result. In addition, thedetermined highest peak point position is sometimes deviated from thecorrect in-focus position due to the optical system's other aberrations(astigmatism, etc.) than the spherical aberration.

FIG. 4 shows how the amplitude of the readout signal changes dependingon the spherical aberration and the defocus. Its distribution has arelatively sharp central peak with many small peripheral pseudo peaks.Around the central peak, it is easy to find the correct in-focusposition since the central peak is not oblique. Adjustment to thecorrect in-focus position can be realized by adjusting both sphericalaberration and defocus alternately so as to reach the highest peak point(the maximum amplitude of the readout signal). The highest peak pointposition relatively stably agrees with the correct in-focus positionregardless of the presence of other aberrations (astigmatism, etc.) Inthe case of an unrecorded disk (not initialized/formatted disk),however, the amplitude of the readout signal cannot be detected since ithas no marks written thereon.

Accordingly, a two-stage adjustment procedure is inevitable to performproper spherical aberration adjustment for an unrecorded disk. Afterboth spherical aberration and defocus are concurrently adjusted so as toroughly maximize the amplitude of the tracking error signal as shown inFIG. 3, marks are written. Then, both spherical aberration and defocusare alternately adjusted so as to finely maximize the amplitude of areadout signal retrieved from the marks as shown in FIG. 4. Thisprocedure is shown in the flowchart of FIG. 5.

It is the correcting signal generator 34 that performs theabove-mentioned two-stage adjustment procedure based on a signal fromthe main sequencer 39. A defocus signal is output as a variation of thefocal position whereas a spherical aberration correcting signal isoutput to the spherical aberration controller 23. Both sphericalaberration correcting signal and defocus signal are concurrentlyadjusted so as to maximize the amplitude of the tracking error signalaccording to the above-mentioned procedure. Then, after marks arerecorded, they are alternately adjusted so as to maximize the amplitudeof the readout signal. By this, the optical system is adjusted toprovide the correct in-focus position where the spherical aberration iscorrected, that is, the spherical aberration is totally corrected.

Note that the spherical aberration correcting signal and the defocussignal can be adjusted by, for example, a two-dimensional search method.An example of a two-dimensional search procedure for this adjustmentwill be described later as an embodiment.

(Effect and Complement)

Since an unrecorded medium with no marks (or pits) can be used as therecording medium (optical disk 8), it is not necessary to record marks(pits) in advance. Therefore, this method is advantageous in cost.

In addition, the optical system required by this method is same inconfiguration as conventional ones except for the spherical aberrationcorrecting mechanism. This is another advantage in cost since theoptical head can directly use parts and circuits for conventionaloptical systems.

Further, since coarse adjustment is made by using the amplitude of thetracking error signal at first, a search for the maximum amplitude ofthe readout signal can be started in the vicinity of the central peak ofthe readout signal. This can prevent the search from converging to apseudo peak of the readout signal. Therefore, this method isadvantageous in adjustment reliability.

In addition, although the highest peak point of the tracking errorsignal may be influenced by other aberrations than spherical aberration,readjustment using the readout signal can automatically set the opticalsystem to a proper in-focus condition. This is also advantageous inadjustment reliability.

That is, this two-stage adjustment procedure enables low cost and highreliability automatic adjustment by: adjusting the optical system so asto maximize the amplitude of the tracking error signal for a rewritableoptical recording medium; recording marks thereon; and adjusting theoptical system so as to maximize the amplitude of the readout signalfrom the marks.

Note that this method may also be applied to a differential push-pullsystem in which another photodetector for detecting a tracking errorsignal is added to the four quadrant photodetectors 26. The differentialpush-pull system use a differential push-pull signal instead of theabove mentioned tracking error signal. The differential push-pull signalcan be generated through the addition or subtraction of the trackingerror signal and the added photodetector. Since this tracking errorsignal is identical in characteristics to the above-mentioned trackingerror signal, the differential push-pull system can be employed in thisadjustment method.

The marks recorded for adjustment may be overwritten or erased after theadjustment is complete. This procedure is shown in the flowchart of FIG.6. This prevents the written marks, required temporally for adjustment,from causing trouble when information is written.

In addition, although a rotary recording medium such as an optical diskis assumed in the description of this embodiment, this adjustment methodprovides the same effect for non-rotary recording media such as a cardtype medium, too. In the case of a non-rotary recording medium, thetracking signal is constituted so as to indicate how much the trackingis deviated from the central line of aligned data written/recorded (onthe recording medium). Like an optical disk, a groove structure isformed on the card type medium so that a tracking error signal can beobtained. The head and circuit configurations shown in the figure areapplicable without any modifications.

In addition, although the liquid crystal aberration corrector 17 isassumed as means to correct the spherical aberration in the descriptionof this embodiment, the liquid crystal corrector may be replaced by acombination of lenses. FIG. 7 shows a configuration in which a movableconvex lens 6 combined with a concave lens 7 is used as the means tocorrect the spherical aberration. In this case, the movable convex lens6 is displaced in proportion to the output of the spherical aberrationcontroller 23. The distance between the lenses is changed in order tocontrol the effective focal distance so as to compensate for the changeof the spherical aberration which depends on the thickness of thesubstrate. The aforementioned spherical aberration and defocusadjustment procedure is also applicable to this configuration withoutmodification.

The aforementioned spherical aberration correcting procedure can beapplied to an unrecorded disk, too. When the spherical aberrationadjustment is made with a recorded (initialized) disk, the adjustmentcan be started from the step of searching for the maximum amplitude ofthe readout signal since marks are already recorded. Accordingly, theadjustment procedure can be designed as shown in the flowchart of FIG. 1where readout signal check is made at first in order to judge whetherthe disk is a recorded disk or an unrecorded disk. Depending on thejudgment, it is decided whether to start the adjustment from the maximumtracking error signal amplitude search step or from the maximum readoutsignal amplitude search step. This branching processing scheme can notonly reduce the time of adjustment with a recorded disk but also performproper spherical aberration adjustment with either disk. Thismeasurement method has the merit of being able to reduce the time spentto adjust the spherical aberration with recorded disks.

Embodiment 2

Two-Dimensional Search Method

An example of a two-dimensional search procedure for sphericalaberration/defocus adjustment according to the present invention isdescribed below with reference to FIGS. 8 through 15.

(Two-Dimensional Search Method for Tracking Error Signal Amplitude)

With reference to FIGS. 8 through 11, the following describes aprocedure for maximizing the amplitude of the tracking error signal.

Firstly, FIG. 8 shows an enlarged central part of the tracking errorsignal's amplitude distribution shown in FIG. 3. FIG. 8 is depicted as acontour map. Note that as compared with FIG. 3, the axis of thespherical aberration is given opposite signs and therefore apparentslopes are opposite.

As mentioned in the description of the first embodiment, thedistribution of the tracking error signal amplitude as a function of thespherical aberration and the defocus resembles a mountain chain having apeak elongated in an oblique direction. Therefore, the highest level fora given aberration differs depending on the defocus. This means thateach time the spherical aberration is changed for peak search, thedefocus must also be changed in order to search for the highest point inan oblique direction.

For example, assume a search is started from white circle (a). Bychanging the spherical aberration at first, point (b) is found at whichthe tracking error signal shows peak amplitude. Since point (b) existson a ridge, adjusting only the defocus either rightward (b1) or leftward(b2) from point (b) results in decreasing the amplitude of the trackingerror signal. To find a point at which the track error signal has ahigher amplitude, it is therefore necessary to move in an obliquedirection, for example, toward (c) or (c′). Further, point (d) is foundfrom (c) and then point (e) is found from point (d) in searching for thehighest peak point corresponding to the maximum amplitude of thetracking error signal.

That is, in order to properly locate the maximum amplitude of thetracking error signal, such two-dimensional oblique search steps must beincluded. Here, the two dimensions respectively correspond to thesubstrate thickness error and the defocus. As shown in FIG. 8, the locusof this search includes oblique lines (b)→(c) and (d)→(e). A search iscalled an oblique search if its locus is an oblique line.

Usually, the amplitude of the tracking error signal fluctuates dependingon the angle of rotation of the disk since the disk has a focusableportion and a less focusable portion caused by partial warps and thelike. Therefore, when detecting the amplitude of the tracking errorsignal, it is often necessary to wait until the disk makes “onerevolution” for each amplitude detection. Increasing the number ofdetections makes longer the total search (adjust) time. Therefore,oblique search is much effective in reducing the total search time sincethe number of detections is decreased.

Note that while the above description includes the expression “tomaximize the amplitude of the tracking error signal”, this does not meanthat the amplitude of the tracking error signal must completely bemaximized. In FIG. 8, the central peak strength (strength at the centerof the cross) is 0.626 (arbitrary strength). As far as the obtainedamplitude is not lower than 0.60, the remaining spherical aberration anddefocus errors can respectively be reduced to within 8 μm (equivalentsubstrate thickness error) and 0.7 μm from the correct in-focusposition. If the adjustment with the amplitude of the tracking errorsignal is complete with such small errors, the subsequent adjustmentwith the readout signal can be started from a position within the footof the central peak, allowing the search to accurately converge to thehighest peak point of the readout signal's amplitude. That is, theexpected effect described in this specification can be attained as faras the obtained amplitude of the tracking error signal is not smallerthan 96% of the maximum value. In this specification, “maximization”includes such rough maximization.

The convergence speed depends on how the search angle is deviated fromthe ideal search angle. Referring to FIG. 9, the convergence speed bythe oblique search is more than twice that by the four-direction searchif the tangent of the search angle is in the range of ±60% of thetangent of the ideal search angle. In addition, if the deviation fromthe ideal search angle is in the range of ±25%, half of the highestconvergence speed (at ±0%) is obtained even at worst. Preferably, thesearch angle is determined so as to fall within such a range from theproper angle.

Ideally, the oblique search angle can be determined according to, forexample, the following proportional expression:

$\begin{matrix}{{\Delta\; z} = {{{- \frac{\left( {n^{2} - 1} \right)}{4n^{3}}} \cdot ({NA})^{2} \cdot \Delta}\; t}} & {{Equation}\mspace{14mu} 1}\end{matrix}$Where, Δz is the defocus, Δt is the substrate thickness error, n is therefractive index of the substrate and NA is the numerical aperture ofthe lens. In this equation, Δz is calculated as the difference betweenthe paraxial image point (Gaussian image point) and the ideal imagepoint, which occurs due to the spherical aberration equivalent tosubstrate thickness error Δt, on the assumption that light is uniformlydistributed in the range of the pupil radius corresponding to numericalaperture NA. When n=1.6 and NA=0.85, the proportion is constant asbelow:

$\begin{matrix}{{\Delta\; z} = {{{{- 0.0688} \cdot \Delta}\; t} = {- \frac{\Delta\; t}{14.5}}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

This means that it is possible to move along a ridge toward the highestpoint of the tracking error signal amplitude if both sphericalaberration and the defocus are changed concurrently by correctionmechanism at a ratio of 14.5 μm (equivalent substrate thickness error)to 1 μm (defocus). However, the above equation is accurate only if thelight flux incident on the lens has a uniform distribution in luminousenergy. If the distribution is not uniform, the constant varies from14.5 since the effective numerical aperture (NA) (generally) decreases.In addition, the constant is also affected by the ratio of the trackinterval to the resolution the beam spot. For example, the constant isas high as 25 in some actual optical heads. The value obtained accordingto the above equation is just for reference. In practice, the searchangle is determined based on actual measurement for each specificallyhead designed optical head.

In addition to spherical aberration, the optical system may also haveother aberrations such as those attributable to the dimensional andpositional errors of components. A distribution of the tracking errorsignal amplitude, depicted as a contour map in FIG. 10, is obtained withthe presence of astigmatism whereas a distribution in FIG. 11 isobtained with the presence of coma aberration. Referring to FIG. 10, thecentral peak of the distribution is shifted left due to astigmatism.This means that adjustment to the highest peak point (maximum amplitudeof the tracking error signal) does not always set the optical system tothe correct in-focus condition. Accordingly, adjustment with theamplitude of the readout signal, as described below, is necessary.

In the first adjustment step to correct the spherical with the amplitudeof the tracking error signal, a search for an optimum amplitude pointcan be done at high speed. Therefore, this method can reduce the waitingtime imposed immediately after loading or during initialization.

(Two-Dimensional Search Method for Readout Signal Amplitude)

With reference to FIGS. 12 through 15, the following describes a searchprocedure for maximizing the amplitude of the readout signal.

Firstly, FIG. 12 shows a central part of the readout signal amplitudedistribution shown in FIG. 4. FIG. 12 is depicted as an enlarged contourmap.

As mentioned in the description of the first embodiment, thedistribution of the readout signal amplitude as a function of thespherical aberration and the defocus has a relatively sharp central peakwith many small peripheral pseudo peaks. Since the central peak is notoblique, it is possible to reach the correct in-focus position (highestcentral peak point) by alternately changing the spherical aberration andthe defocus.

For example, a search is started from white circle (e). By changing thespherical aberration at first, point (f) is found at which the readoutsignal shows the maximum amplitude. From this point, point (g) nearer tothe highest peak point can be found as a higher amplitude point only byadjusting the defocus. This indicates that if the start point is in thevicinity of the central peak, it is possible to reach the highest peakpoint of the readout signal amplitude by alternately changing thespherical aberration and the defocus so as to increase the amplitude ofthe readout signal. That is, adjustment to the correct in-focus positioncan be realized by alternately adjusting the spherical aberration andthe defocus toward the highest peak point (maximum amplitude of thereadout signal). In the case of the readout signal amplitude, thetwo-dimensional search can be done substantially at the highest speed bysimple alternate adjustment of the spherical aberration and the defocus.The locus of this search is rectangular in the two-dimensional plotplane as indicated by the arrows of FIG. 12. The search is called arectangular search if its locus is rectangular.

In addition to spherical aberration, the optical system may also haveother aberrations such as those attributable to the dimensional andpositional errors of components. A distribution of the readout signalamplitude, depicted as a contour map in FIG. 13, is obtained with thepresence of astigmatism whereas a distribution in FIG. 14 is obtainedwith the presence of coma aberration. In the case of the readout signal,the peak center of the distribution agrees well with the center of thegraph regardless of such aberration. This means that adjustment to thecorrect in-focus position is possible by searching for the highest peakpoint (maximum amplitude of the readout signal). That is, the resultingerror of coarse adjustment with the tracking an error signal canproperly be corrected by fine adjustment with the readout signal.

Contour maps indicating distributions of the readout signal amplitude inFIGS. 15A through 15D are respectively obtained by changing the periodof the written mark pattern. The written pattern, from which the readoutsignal is retrieved, is a repetition of a mark portion followed by aspace portion (no mark recorded) wherein the length ratio is 1:1. Themark period (total length of a mark portion and a space portion) ischanged to 1.5 times, 2 times, 4 times and 6 times the track interval,as shown in FIGS. 15A, 15B, 15C and 15D, respectively. Usually, thetrack interval is set 10 to 20% smaller than the size of the beam spotfrom the viewpoint of efficiency in terms of recording density.Accordingly, the track interval in data areas in a typical opticalrecording disk/medium reflects the resolution of the beam spot.

The distribution in FIG. 15A, which is obtained from marks recorded withthe shortest mark period, is inclined a little. For the same reason asthe description of the two-dimensional search for the maximum amplitudeof the tracking error signal, the rectangular search, namely, thealternate adjustment of the spherical aberration and the defocus,somewhat slows down. On the other hand, the peak center (maximumamplitude point) of the distribution of FIG. 15D obtained with thelongest mark period is shifted a little to the lower right side(deviated from the correct in-focus position). This indicates that theappropriate recorded mark interval is 2 to 4 times the track intervalwhen the maximum amplitude of the readout signal is to be sought tolocate the correct in-focus position. In addition, this range of markintervals facilitates adjustment since the contour density around thepeak is high. A high contour density means that the adjustmentsensitivity is high due to a large change of the readout signalamplitude caused by a change of the spherical aberration/defocus. Thebest mark interval is about 3 times between 2 times and 4 times.

Thus, the period of the written mark is set to an appropriate length. Arepetitive mark pattern is recorded, as the written mark pattern, with amark period equal to 2-4 times the track interval in the data area,whereby adjustment to the correct in-focus position can easily berealized by searching for the maximum amplitude of the readout signal.Since high adjustment sensitivity and high noise immunity can berealized by using such a mark pattern, this method carries the advantagethat the cost of the adjustment control mechanism can be lowered.

The reason that the mark length is treated above in terms of the trackinterval is that the track interval reflects the size of the beam spotand therefore can be considered as one of the criteria for theresolution of the beam spot.

As mentioned so far, the spherical aberration and the defocus areadjusted in a two-dimensional plot plane where one axis represents thedefocus while the other axis the correction of the spherical aberration,as shown in FIGS. 8 through 15. Oblique search is repeated at first soas to maximize the amplitude of the tracking error signal and thenrectangular search is repeated so as to maximize the amplitude of thereadout signal. Switching the search style makes it possible to reducethe search time and secure adjustment reliability.

(Effect and Complement)

Changing the search style is effective in raising the adjustment speedsince the distribution of the tracking error signal amplitude isdifferent in shape from that of the readout signal amplitude. Thespherical aberration and the defocus are adjusted in a two-dimensionalplot plane where one axis represents the defocus while the other axisthe correction of the spherical aberration. The oblique search (notparallel to the two axes) is repeated at first so as to maximize theamplitude of the tracking error signal and then the rectangular search(parallel to either axis) is repeated so as to maximize the amplitude ofthe readout signal. This makes it possible to adjust the optical systemboth reliably and quickly as a whole.

This method is applicable to an unrecorded recording medium and canraise the total measurement speed while securing higher reliabilityadjustment of the spherical aberration. This makes it possible toefficiently adjust the spherical aberration and the defocus andtherefore remarkably reduce the time required to adjust the opticalaxis. In addition, this results in providing the advantage that thewaiting time imposed immediately after loading or during initializationcan be shortened.

Note that in some case, the tilt (of the optical head relative to therecording medium) is adjusted in addition to the spherical aberrationand the defocus. Such a system may be configured so as to perform threeor four-dimensional search including the tilt (1 or 2 degrees offreedoms). It is also possible to adjust two quantities, for example,the spherical aberration and the defocus, in the two-dimensional plotplane with the remaining one or two quantities fixed. In the later case,the spherical aberration and the defocus can be adjusted by the obliquesearch and then by the rectangular search in the same manner asmentioned above.

In addition, since the spherical aberration can properly be adjusted tothe optimum point regardless of the presence of astigmatism in theoptical system, this method is applicable to a medium having thickplastic layers (cover layer and substrate layer) which are likely tocause aberration. That is, this method carries the advantage that higherdensity recording is possible since a stable beam spot can be obtainedregardless of aberration.

Embodiment 3

(Adjustment of Spherical Aberration by Using Interpolative Values)

With reference to FIGS. 2 and 16 through 21, the following describesconfigurations of optical information recording apparatus that correctspherical aberration for a recording medium having a transparent layerwhose thickness varies from place to place on the medium.

(Correction for Single Recording Layer, or One and the Same RecordingLayer)

Firstly, referring to FIGS. 16 and 17, the following describes theconfiguration of an optical information recording apparatus thatcorrects the spherical aberration so as to compensate for the thicknesserror of the transparent layer formed on the recording medium. It isassumed either that the recording medium has a single recording layer orthat the recording medium has plural recording layers but correction ismade for one of them.

FIG. 16 shows a recording disk medium having a single recording layer. Aspherical aberration adjustment procedure, shown in FIG. 17 (flowchart),is applied to this recording medium. The optimum spherical aberrationand defocus are measured at inner point A and outer point B by using themethod mentioned in the description of the first and second embodiments.Ideally, point A is located in the innermost area whereas point B islocated in the outermost area. Assume that SA1 and DF1 respectivelydenote the spherical aberration and defocus determined for point A.Likewise, SA2 and DF2 respectively denote the spherical aberration anddefocus determined at point B.

By using them, spherical aberration SAx and defocus DFx at arbitraryradius Px on the recording medium (disk) are determined by interpolationas below:

$\begin{matrix}\begin{matrix}{{SAx} = {{{{SA}1}\;\frac{{{Px}2} - {Px}}{{{Px}2} - {{Px}1}}} + {{{SA}2}\;\frac{{Px} - {{Px}1}}{{{Px}2} - {{Px}1}}}}} \\{{DFx} = {{{{DF}1}\;\frac{{{Px}2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} + {{DF}\; 2\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}}}\end{matrix} & {{Equation}\mspace{14mu} 3}\end{matrix}$

In the above equation, Px1, Px2 and Px are the radii of arbitrary pointson the disk, respectively. A specific implementation of this procedureis described below along with the configuration of FIG. 2. The mainsequencer 39 gives Px, P1 and P2 to the correcting signal generator 34wherein Px is the radius of a track for data read/write and P1 and P2are the radii of inner point A and outer point B for which measurementwas already made. The correcting signal generator 34 calculatesspherical aberration SAx and defocus DFx for the radius Px trackaccording to the above equation and outputs them respectively to thespherical aberration controller 23 and the defocus offset adder 31. Inthis manner, spherical aberration is corrected for any position on therecording medium (disk) by linear approximation.

This method is also applicable to not only non-rotary recording mediasuch as a recording card medium but also multilayer recording diskmedia. If information is multi-dimensionally stored in X and Ydirections, radial (track number) and stacking directions or the like,interpolation is made in each direction to calculate optimum sphericalaberration and defocus for arbitrary coordinates in the multidimensionalcoordinate system. That is, the spherical aberration and defocus at anyposition in any shaped recording medium can be corrected for dataread/write by linear approximation in substantially the same manner asfor a single-layer recording disk.

In this configuration, optimum spherical aberration correction (andoptimum defocus for the objective lens) is measured at inner and outertracks on the medium. Optimum values for intermediary informationread/write tracks are calculated by interpolation based on the optimumvalues measured for the inner and outer tracks and the calculated valuesare used to correct/control the defocus and spherical aberration.

In the case of a multilayer optical disk medium, the adjustmentprocedure is configured as described below.

FIG. 18 shows a multilayer recording disk medium. A spherical aberrationadjustment procedure, shown in FIG. 19 (flowchart), is applied to thisrecording medium. The medium has N recording layers stacked in direction5 at regular intervals. Using the method mentioned in the description ofthe first and second embodiments, optimum spherical aberration anddefocus are measured at inner and outer points in the top layer (1stlayer) and then at the corresponding points in the bottom layer (Nthlayer). Assume that SA1T, SA2T, SA1B, SA2B, DE1T, DF2T, DF1B and DF2Bdenote the respective measurement results.

By using them, spherical aberration SAxz and defocus DFxz for arbitraryposition Px in the Pzth layer are calculated by interpolation as below:

$\begin{matrix}\begin{matrix}{{SAxz} = {{\left( {{{SA}\; 1T\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} + {{SA}\; 2T\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}} \right)\frac{N - {Pz}}{N - 1}} +}} \\{\mspace{79mu}{\left( {{{SA}\; 1B\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} + {{SA}\; 2B\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}} \right)\frac{{Pz} - 1}{N - 1}}} \\{{DFxz} = {{\left( {{{DF}\; 1T\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} + {{DF}\; 2T\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}} \right)\frac{N - {Pz}}{N - 1}} +}} \\{{\left( {{{DF}\; 1B\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} + {{DF}\; 2B\;\frac{{Px} - {Px1}}{{Px2} - {Px1}}}} \right)\frac{{Pz} - 1}{N - 1}}}\end{matrix} & {{Equation}\mspace{14mu} 4}\end{matrix}$

A specific implementation of this procedure is described below alongwith the configuration of FIG. 2. The main sequencer 39 has the means tostore Px, Pz, wherein Px and Pz designate a track in the recordingmedium for data read/write and SA1T, SA2T, SA1B, SA2B, DF1T, DF2T, DF1Band DF2b are spherical aberration and defocus values measured alreadyfor the top and bottom layers. The main sequencer 39 gives them to thecorrecting signal generator 34. The correcting signal generator 34calculates spherical aberration SAxz and defocus DFxz for radius Px inthe Pzth layer according to the above equation and outputs themrespectively to the spherical aberration controller 23 and the defocusoffset adder 31. In this manner, spherical aberration is corrected forany position in the recording medium by linear approximation.

This configuration has the means to store the optimum sphericalaberration correction (and optimum defocus for the objective lens)measured at inner and outer tracks on the medium. Optimum values forintermediary information read/write tracks are calculated byinterpolation based on the optimum values measured for the inner andouter tracks and the calculated values are used to correct/control thedefocus and spherical aberration.

For the layer stacking direction, this configuration has the means tostore the optimum spherical aberration correction measured for the topand bottom layers. When moving across plural recording layers, thespherical aberration is optimized for the target layer by interpolationbased on the optimum values measured for the top and bottom layers.

In the case of a non-rotary multilayer medium, the adjustment procedureis configured as described below.

FIG. 20 shows a multilayer recording card medium. A spherical aberrationadjustment procedure, shown in FIG. 21 (flowchart), is applied to thisrecording medium 2. The medium has positions Px in X-direction 3,positions Py in Y-direction 4, and N recording layers stacked indirection 5 at regular intervals. Data is read/write from/to therecording layer at Pz-layer. Using the method mentioned in thedescription of the first and second embodiments, optimum sphericalaberration and defocus are measured at the four corners (Px1, Py1),(Px2, Py1), (Px1, Py2) and (Px2, Py2) in the top layer (1st layer) andthen at the corresponding points in the bottom layer (Nth layer). Assumethat SA1T, SA2T, SA3T, SA4T, DF1T, DF2T, DF3T, DF4T, SA1B, SA2B, SA3B,SA4B, DF1B, DF2B, DF3B and DF4 respectively denote the correspondingmeasurement results.

By using them, optimum spherical aberration SAxyz and defocus DFxyz forarbitrary position (Px, Py, Pz) in the recording medium are calculatedby interpolation as below:

$\begin{matrix}\begin{matrix}{{SAxyz} = {{\begin{pmatrix}{{{SA}\; 1T\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{SA}\; 2T\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{{Py}\; 2} - {Py}}{{{Py}\; 2} - {{Py}\; 1}}\frac{N - {Pz}}{N - 1}} +}} \\{\mspace{95mu}{{\begin{pmatrix}{{{SA}\; 3T\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{SA}\; 4T\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{Py} - {{Py}\; 1}}{{{Py}\; 2} - {{Py}\; 1}}\frac{N - {Pz}}{N - 1}} +}} \\{\mspace{95mu}{{\begin{pmatrix}{{{SA}\; 1B\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{SA}\; 2B\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{{Py}\; 2} - {Py}}{{{Py}\; 2} - {{Py}\; 1}}\frac{{Pz} - 1}{N - 1}} +}} \\{\mspace{95mu}{\begin{pmatrix}{{{SA}\; 3B\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{SA}\; 4B\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{Py} - {{Py}\; 1}}{{{Py}\; 2} - {{Py}\; 1}}\frac{{Pz} - 1}{N - 1}}} \\{{DFxyz} = {{\begin{pmatrix}{{{DF}\; 1T\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{DF}\; 2T\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{{Py}\; 2} - {Py}}{{{Py}\; 2} - {{Py}\; 1}}\frac{N - {Pz}}{N - 1}} +}} \\{\mspace{95mu}{{\begin{pmatrix}{{{DF}\; 3T\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{DF}\; 4T\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{Py} - {{Py}\; 1}}{{{Py}\; 2} - {{Py}\; 1}}\frac{N - {Pz}}{N - 1}} +}} \\{\mspace{95mu}{{\begin{pmatrix}{{{DF}\; 1B\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{DF}\; 2B\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{{Py}\; 2} - {Py}}{{{Py}\; 2} - {{Py}\; 1}}\frac{{Pz} - 1}{N - 1}} +}} \\{\mspace{95mu}{\begin{pmatrix}{{{DF}\; 3B\;\frac{{{Px}\; 2} - {Px}}{{{Px}\; 2} - {{Px}\; 1}}} +} \\{{DF}\; 4B\;\frac{{Px} - {{Px}\; 1}}{{{Px}\; 2} - {{Px}\; 1}}}\end{pmatrix}\frac{{Py} - {Py1}}{{{Py}\; 2} - {Py1}}\frac{{Pz} - 1}{N - 1}}}\end{matrix} & {{Equation}\mspace{14mu} 5}\end{matrix}$

A specific implementation of this procedure is described below alongwith the configuration of FIG. 2. The main sequencer 39 gives Px, Py,Pz, Px1, Px2, Py1, Py2 and N to the correcting signal generator 34wherein Px, Py and Pz designate a position in the recording medium fordata read/write, Px1, Px2, Py1 and Py2 designate the four corner pointsand N defines the number of layers. The correcting signal generator 34calculates optimum spherical aberration SAxyz and defocus DFxyz for thedata read/write position according to the above equation and outputsthem respectively to the spherical aberration controller 23 and to thedefocus offset adder 31. In this manner, spherical aberration iscorrected for any position in the recording medium by linearapproximation.

For the X and Y directions, this configuration has the means to storethe optimum spherical aberrations (and optimum defocuses for theobjective lens) measured at the four corners. Optimum values for anintermediary information read/write position in a recording layer arecalculated from the optimum values by interpolation based on the X and Ydistances from the four corners and the calculated values are used tocorrect/control the defocus and spherical aberration.

For the layer stacking direction Z, this configuration has the means tostore the optimum spherical aberrations measured for the top and bottomlayers. When moving across plural recording layers, the sphericalaberration is optimized for the target layer by interpolation based onthe optimum values measured for the top and bottom layers.

(Effect)

In this method, spherical aberration can be corrected by linearinterpolation for any position as mentioned above. In the case of a diskmedium, spherical aberration can be optimized at any track or radius. Inthe case of a multilayer disk, spherical aberration can also be doneproperly when access jumps across plural layers. Since sphericalaberration can properly be adjusted with these recording media, thisadjustment method allows signals to be recorded/reproduced properlyto/from these media.

(Total Effect)

As mentioned so far, the present invention allows an optical informationrecording apparatus to accurately adjust the spherical aberration morequickly and more reliably when any position is accessed.

Although many optical head structures have been proposed in order toallow optical information recording apparatus to correct sphericalaberration, this method is advantageous in cost since this method candirectly be applied to most of the existing optical heads provided withtracking error signal detecting function.

In addition, unlike the method disclosed in Japanese Patent Laid-openNo. 2002-358677 which dynamically drives the spherical aberrationdetector/controller based on a diverged light beam, this method canreduce the total circuit noise since it is not necessary to incorporatemany photo-detectors and photo-amplifiers.

Therefore, it is possible to provide a lower cost and higher reliabilityoptical disk apparatus (optical information recording apparatus) capableof correcting the spherical aberration.

1. An optical information recording apparatus which optically reads andwrites information from and to a recording medium, comprising: a firstdetector for detecting amplitude of a readout signal; a second detectorfor detecting amplitude of a tracking error signal; a first adjustor foradjusting spherical aberration; a second adjustor for adjusting defocusof an objective lens; an oblique search means for changing the sphericalaberration and the defocus obliquely in a two-dimensional rectangularcoordinate system whose respective axes represent the defocus and thespherical aberration; a rectangular search means for changing thespherical aberration and the defocus rectangularly in thetwo-dimensional rectangular coordinate system; and a switching means forswitching the oblique search means and the rectangular search means whenadjusting coarsely and finely; wherein: the spherical aberration and thedefocus are adjusted at first obliquely by the oblique search means soas to maximize the amplitude of the tracking error signal and thenadjusted rectangularly by the rectangular search means so as to maximizethe amplitude of the readout signal, the recording medium is anon-rotary recording medium, said apparatus further comprises a memoryfor storing optimum spherical aberration values and optimum defocusvalues which are respectively for four corners on the recording medium,and the optimum spherical aberration and defocus values for aninformation read/write position are calculated from the stored optimumvalues by interpolation based on ratios in terms of distances from thefour corners.
 2. An optical information recording apparatus according toclaim 1, wherein: in case that an initialized recording medium isinserted, the adjustment is started from optimization for the amplitudeof the readout signal; and in case that a not initialized recordingmedium is inserted, the adjustment is started from optimization for theamplitude of the tracking error signal.
 3. An optical informationrecording apparatus which optically reads and writes information fromand to a recording medium, comprising: a first detector for detectingamplitude of a readout signal; a second detector for detecting amplitudeof a tracking error signal; a first adjustor for adjusting sphericalaberration; a second adjustor for adjusting defocus of an objectivelens; an oblique search means for changing the spherical aberration andthe defocus obliquely in a two-dimensional rectangular coordinate systemwhose respective axes represent the defocus and the sphericalaberration; and a rectangular search means for changing the sphericalaberration and the defocus rectangularly in the two-dimensionalrectangular coordinate system; wherein the spherical aberration and thedefocus are adjusted by the oblique search means so as to maximize theamplitude of the tracking error signal from an unrecorded rewritableoptical recording medium, marks are recorded on the optical recordingmedium, and then the spherical aberration and the defocus are adjustedby the rectangular search means so as to maximize the amplitude of thereadout signal, wherein the recorded marks constitute a repetitivepattern whose mark interval is 2 to 4 times a track interval in a dataarea.